Woo Dong Jang

Enhanced photodynamic cancer treatment by supramolecular nanocarriers charged with dendrimer phthalocyanine.

Photodynamic therapy (PDT) is a promising method for the localized treatment of solid tumors. In order to enhance the efficacy of PDT, we have recently developed a novel class of photosensitizer formulation, i.e., the dendrimer phthalocyanine (DPc)-encapsulated polymeric micelle (DPc/m). The DPc/m induced efficient and unprecedentedly rapid cell death accompanied by characteristic morphological changes such as blebbing of cell membranes, when the cells were photoirradiated using a low power halogen lamp or a high power diode laser. The fluorescent microscopic observation using organelle-specific dyes demonstrated that DPc/m might accumulate in the endo-/lysosomes; however, upon photoirradiation, DPc/m might be promptly released into the cytoplasm and photodamage the mitochondria, which may account for the enhanced photocytotoxicity of DPc/m. This study also demonstrated that DPc/m showed significantly higher in vivo PDT efficacy than clinically used Photofrin (polyhematoporphyrin esters, PHE) in mice bearing human lung adenocarcinoma A549 cells. Furthermore, the DPc/m-treated mice did not show skin phototoxiciy, which was apparently observed for the PHE-treated mice, under the tested conditions. These results strongly suggest the usefulness of DPc/m in clinical PDT.

Polymeric supramolecular systems for drug delivery

Recent advances in supramolecular chemistry have had significant influence on the biomedical applications of materials chemistry. Supramolecular systems are based on weak and reversible non-covalent interactions, such as hydrogen bonding, metal coordination, hydrophobic attractions, van der Waals forces, π–π, and electrostatic interactions. Because of the weak and reversible nature of the molecular interactions in self-assembled supramolecular systems, they are excellent candidates for the design of drug delivery systems (DDS). In DDS, therapeutic agents can be temporarily encapsulated into the carrier vehicles and released at a specific site or with designated timing. Using DDS, the effectiveness of existing drugs can be optimized, which sometimes provides new indications. DDS must have not only optimal drug loading capacities and release properties, but also be biocompatible with low toxicity. Many types of biocompatible polymeric materials have already been developed for self-assembled drug formulations. Current studies on DDS are aiming at target-specific delivery of therapeutic agents and stimuli-responsive drug release. In this feature article, we will overview polymeric supramolecular systems for target-specific drug delivery and stimuli-responsive drug release.

Thermodynamics of DNA Condensation Induced by Poly(ethylene glycol)-block-polylysine through Polyion Complex Micelle Formation

Isothermal titration calorimetry (ITC) was carried out to explore the condensation process of plasmid DNA (pDNA) molecules induced by poly(ethylene glycol)-poly(L-lysine) block copolymer (PEG-PLL) as a condensing agent. The ITC curves measured can be divided into two distinctive endothermic binding processes: the first was the binding of PEG-PLL to the elongated pDNA, and the second was the binding that accompanied the pDNA conformational transition. The thermodynamic parameters were obtained by fitting each ITC curve using our recently developed fitting method. The binding of PEG-PLL to the pDNA was accompanied by a small increase in enthalpy, a large increase in entropy, and a large decrease in free energy. The binding stabilized as the polymerization degree of PLL on PEG-PLL increased and the salt concentration decreased. Changes in the thermodynamic parameters are discussed in relation to both the polymerization degree of PLL on PEG-PLL and the salt concentration.

A2E, a Pigment of the Lipofuscin of Retinal Pigment Epithelial Cells, Is an Endogenous Ligand for Retinoic Acid Receptor

Lipofuscin contains fluorophores, which represent a biomarker for cellular aging. Although it remains unsubstantiated clinically, experimental results support that the accumulation of lipofuscin is related to an increased risk of choroidal neovascularization due to age-related macular degeneration, a leading cause of legal blindness. Here, we report that a major lipofuscin component, A2E, activates the retinoic acid receptor (RAR). In vitro experiments using luciferase reporter assay, competitional binding assay, analysis of target genes, and chromatin immunoprecipitation (ChIP) assay strongly suggest that A2E is a bona fide ligand for RAR and induces sustained activation of RAR target genes. A2E-induced vascular endothelial growth factor (VEGF) expression in a human retinal pigment epithelial cell line (ARPE-19) and RAR antagonist blocked the up-regulation of VEGF. The conditioned medium of A2E-treated ARPE-19 cells induced tube formation in human umbilical vascular endothelial cells, which was blocked by the RAR antagonist and anti-VEGF antibody. These results suggest that A2E accumulation results in the phenotypic alteration of retinal pigment epithelial cells, predisposing the environment to choroidal neovascularization development. This is mediated through the agonistic function of A2E, at least in part. The results of this study provide a novel potential therapeutic target for this incurable condition.

Polymer–metal complex micelles for the combination of sustained drug releasing and photodynamic therapy

Polymer–metal complex micelles (PMCMs) containing cisplatin (cis-dichlorodiammineplatinum(II), CDDP), an anticancer drug, were prepared by a coordination bond of CDDP to dendrimer phthalocyanine (DPc) and poly(ethylene glycol)-block-poly(L-aspartic acid) (PEG-PLAn; molecular weight of PEG segment = 12 000 g mol−1; polymerization degrees of aspartic acid segment n = 68, 96). Transmission electron microscopy (TEM) and laser light scattering (LLS) exhibited formation of unimodal PMCM68 and PMCM96 with average sizes of 108 and 135 nm, respectively. PMCMs were very stable in 10 mM phosphate buffer solution (PBS) without NaCl to maintain their shape and size over a month. However, PMCMs slowly released CDDP when they were incubated in physiological saline PBS solution at 37 °C. Upon laser light irradiation, generation of singlet oxygen was detected by photo-luminescence observation. The PMCMs would be effective nano-devices for anticancer drug carriers with sustained drug release and photodynamic therapy (PDT).

Protein-conjugated, glucose-sensitive surface using fluorescent dendrimer porphyrin

A multi-functional dendrimer-coated surface has been prepared for the effective protein immobilization and detection of protein activity. The silicon surface was first modified with positively-charged amino groups using 3-aminopropyltriethoxysilane (APTES), and subsequently coated with ionic dendrimer porphyrin (DP) by electrostatic interaction. Fluorescence and atomic force microscopy (AFM) studies showed that the dendrimer was homogeneously coated on the APTES-modified silicon surface as dome-shaped features that protruded 1.0–2.5 nm above the surface and had diameters ranging from 50 nm to 100 nm. The dendrimer-modified surface showed a higher capacity to covalently bind proteins, compared to the control surfaces, and the protein activity was higher by a factor of two. Using the fluorescent property of the porphyrin core, the relative amounts of dendrimer and the enzyme-catalyzed reactions on the dendrimer-coated surface were examined by fluorescence microscopy. Glucose oxidase (GOX)-mediated glucose oxidation quenched fluorescence emission from the focal porphyrin core through a peroxidase-coupled system and from the quantitative relationship between quenching and glucose concentration, the GOX-catalyzed reaction could be characterized.

A2E, a component of lipofuscin, is pro-angiogenic in vivo

A recent study in vitro demonstrated that a major lipofuscin component, A2E, serves as a retinoic acid receptor ligand. The current study investigated the effects of A2E on retinal pigment epithelial (RPE) cells in vivo and was performed to extend the understanding of the effects of A2E. Firstly, subretinal injection of A2E was performed and 3 weeks after the injection, and it was demonstrated that subretinal injection of A2E induced RPE cell death, and concomitant upregulation of vascular endothelial growth factor (VEGF) in the RPE and choroid. The upregulation of VEGF was attenuated by an RARα antagonist. Next we performed laser photocoagulation in mice that accumulated A2E either after subretinal injection, by Ccl2 gene knockout or by aging demonstrated that mice that accumulated A2E in the RPE, which showed higher rates of choroidal neobascularization (CNV) formation after weak laser injury than the controls and the formation of CNV was inhibited by an RARα antagonist in all models tested. The data suggest that A2E accumulation induces RPE cell death, and concomitant increase of VEGF. Accumulation of A2E alone is not sufficient to induce CNV in vivo, but induces the expression of VEGF in RPE and choroid. The mice that accumulated A2E in RPE cells are vulnerable to CNV development via RAR activation, at least in part. J. Cell. Physiol. 220: 469–475, 2009.

Dendrimer porphyrin-terminated polyelectrolyte multilayer micropatterns for a protein microarray with enhanced sensitivity

Through a combination of layer-by-layer (LbL) self-assembly (SA) and lift-off methods, a dendrimer-coated polyelectrolyte multilayer micropattern was prepared for protein microarrays. A silicon substrate was patterned with a photoresist thin film using conventional photolithography, and then poly(ethyleneimine) (PEI) and poly(sodium 4-styrenesulfonate) (PSS) were alternatively deposited onto the substrate surface using spin-assisted self-assembly. A well-defined multilayer microarray was produced by subsequent removal of the photoresist template by a lift-off process. Dendrimer porphyrin (DP) was successively immobilized onto the PEI-terminated micropatterns via electrostatic interactions between the negatively-charged DPs and positively-charged PEI segments. Because of strong fluorescence from focal porphyrins, the homogeneous covering of DPs onto the multilayer micropatterns was easily confirmed using fluorescence microscopy. Atomic force microscopy (AFM) also showed morphological change of micropatterned surfaces by DP immobilization. Based on these results, IgG was immobilized on the DP-coated protein microarrays, and immunoassays were performed to demonstrate that the DP-coated microarrays yielded a higher fluorescence signal and were more sensitive than the control microarrays that were coated with linear PAA polymer instead of DP due to the multiple functional groups present on the DP-coated arrays and their increased surface area relative to control microarrays.

Synthesis of multi-porphyrin dendrimer as artificial light-harvesting antennae

To mimic bacterial light-harvesting antenna complexes, a series of dendritic multiporphyrin arrays, nPZn-PFB (n = 2, 4; cone-shaped dendrimers, n = 8, 16; star-shaped dendrimers), were synthesized and characterized by 1H NMR and MALDI-TOF-MS spectroscopy. Photoinduced energy-transfer efficiency (ΦET) from peripheral Zn porphyrin (PZn) units to an inner core free-base porphyrin (PFB) in the dendrimers was evaluated by fluorescence measurement. Both star- and cone-shaped multi-porphyrin arrays exhibited significantly high efficiency energy transfer from the photoexcited PZn units to the energy-accepting PFB, where the star-shaped dendrimers, 8PZn-PFB (94%) and 16PZn-PFB (88%), had a slightly higher efficiency than those of the cone-shaped dendrimers, 2PZn-PFB (92%) and 4PZn-PFB (80%), respectively.

Photophysical properties of composite film of dendron-appended porphyrin and fullerene[60]

Dendron-appended porphyrin (den-por) and C60 (den-C60) were synthesized for the application of photovoltaic materials. The composite films of den-por and den-C60 were subjected to absorption and photoluminescence spectroscopic measurements. We determined that solid-state film, spin-coated with a blend of den-por and den-C60 at weight ratio 1:0.5, showed an efficient photoluminescence quenching via donor-to-acceptor electron transfer.